All the time. Makes life much easier. Although I think you still need to learn how to mark them out if your an apprentice.
undercut a fair bit, but if I have time on job I will scribe. in my book there's a BIG difference between those who can properly scribe architraves etc yet undercuts because it's quicker etc than those who undercut because they don't know how to scribe.
I only got a Fein about a month ago... Been undercutting since but that's mainly to play with the new tool!
Always undercut looks neater by far, scribing arcs takes ages to get it right especially if it's busy design, I know a fitter that's got lots of cut offs of different types of arcs and he traces the design onto a tile.
I under cut every thing that can be even the curve on a bull nose some times! Its quick & neat so why not ?